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737-500 missing in Indonesia

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737-500 missing in Indonesia

Old 14th Apr 2021, 14:49
  #781 (permalink)  
 
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While you may be correct in your "what if" it is premature to assume this, as part of this accident, until the CVR summary is released.
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Old 16th Apr 2021, 12:22
  #782 (permalink)  
 
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Seattle Times reporting that lawsuit has been filed in State court in Washington on behalf of 16 families who lost loved ones in the accident. News article indicates that the complaint filed in court points to autothrottle problem and also cites past instances of same.

Excerpt from article:
The lawsuit "cites a list of previous incidents involving malfunctions of the 737 autothrottle system, arguing that this history suggests the system should have been redesigned.“Specifically, the automatic throttle can stick and thereby cause significant differences in power between engines, resulting in a loss of control of the aircraft,” the lawsuit states. The plaintiffs further allege that “Boeing did not provide adequate warnings and instructions about how to respond to a failure in the automatic throttle.”

Another excerpt:
This specific 737 had been parked for nine months last year due to the COVID-19 pandemic air travel downturn. The Indonesian aviation regulators issued a new certificate of airworthiness in mid-December 2020 that allowed it to return to service.

According to the preliminary report into the crash by the Indonesian National Transportation Safety Committee (“KNKT”), maintenance logs show that pilots repeatedly reported issues with the autothrottle in the days before the fatal flight and technicians attempted to rectify the problem by cleaning switches and connectors.

One of the safety regulations introduced after the older 737 planes were certified requires that a jet’s automated systems be designed to give pilots a smooth transition if for any reason they disengage and revert to manual flight.

If automated systems disengage, the jet must not abruptly shift its behavior in such a way as to require unusual pilot skill or strength to maintain control.

In the Sriwijaya crash, after an autothrottle malfunction causing unequal thrust between the two engines had been ongoing for some time, the automated systems eventually disengaged. The plane immediately rolled to an angle of 45 degrees and the pilots lost control, according to the preliminary report.
[end of article excerpt]

Perhaps interesting timing here, in that the plaintiffs' attorneys filed the suit after news the CVR has been recovered, but before knowing what information it may reveal or even whether recorded information survived the crash and oceanic immersion.
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Old 16th Apr 2021, 13:38
  #783 (permalink)  
 
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WillowRun 6-3

"Perhaps interesting timing here, in that the plaintiffs' attorneys filed the suit after news the CVR has been recovered, but before knowing what information it may reveal or even whether recorded information survived the crash and oceanic immersion."

What would be the advantage, if any, of filing a suit during that (relatively narrow) window ?
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Old 16th Apr 2021, 16:43
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Might just ensure that any future clients will use this legal firm and they waited for the CVR to be recovered since without it there is no concrete definitive evidence and the CVR can only improve that situation.
Did you think the legal profession in the US was all about pure objective truth etc? Nope, money
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Old 16th Apr 2021, 17:53
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Implying a lot of cynicism on the part of these attorneys.....the search for the CVR had gone on much longer than for the FDR. No doubt the complaint had been in the works for some time; it refers to the preliminary report which has been out for several weeks.

Perhaps they speculated there was some chance the CVR's content could undercut their claims, so better to get their complaint on file, hoping to hedge against the (possibly) unhelpful content. Also as sceh said, being first to file can be beneficial for gaining other clients.
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Old 16th Apr 2021, 18:39
  #786 (permalink)  
 
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WillowRun 6-3

The article also states that the system WAS redesigned in later models. Further, that particular airplane had a history of autothrottle problems ever since it was brought out of storage. Given that fact, it would seem prudent that the PILOTS would be guarding the throttles at every transition AND be on the alert for any split. That is, IF they even CHOSE to use the autothrottles at all!

IMO, the PILOTS and airline maintenance personnel were solely at fault for failing to resolve and/or account for a recurring problem.
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Old 16th Apr 2021, 20:08
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Wow, did they design and certify this system?
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Old 16th Apr 2021, 20:11
  #788 (permalink)  
 
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Autothrottle

I think that is a premature statement. Do we know that the pilots were briefed about the autothrottle problems?
If yes I would be surprised that they are overwhelmed by such a simple problem.
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Old 16th Apr 2021, 22:30
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I posted about this previously, but it's many pages back so I'll go there again:
The 737-3/4/500 used CFM56-3 engines - cable controlled (not FADEC). Cable controlled engines are subject to excessive down stream cable loads due to things like damaged push/pull cables, corroded or seized pulleys, etc. These high cable loads can overcome the friction clutches that connect the system to the auto throttle drive, allowing the throttle to slip and not respond to auto throttle inputs. It's not a design flaw in so much as it's an overall system limitation when using cable controlled engines with an auto throttle since there needs to be some sort of clutch mechanism to allow manual override of the auto throttle.
Given this aircraft had recently come out of storage, and apparently been experiencing this issue since it came out of storage. My guess is they had excessive cable loads on one throttle due to corrosion while the aircraft was stored. Checking/cleaning connectors won't do anything to correct a damaged throttle cable system - maintenance has to actually go and troubleshoot the cause of the high loads.

The 737NG series uses FADEC CFM56-7 engines - FADEC engines are not susceptible to this sort of problem since they don't have throttle cables.

Last edited by tdracer; 16th Apr 2021 at 22:58.
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Old 16th Apr 2021, 22:40
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EDLB

If they read the maintenance logs, they knew about the problem. If they didn't read the logs, they were derelict in their duty.
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Old 16th Apr 2021, 22:48
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I’m not a pilot (my Dad was) but, if I’m flying an aircraft w misbehaving auto-throttles, would I not at minimum 1) watch the throttles closely during climb and/or 2) have my hand on the throttle quad at all times such that even if I was looking elsewhere I would feel the split?
I know it’s easy for a non-pilot like me to say, but....any comments?
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Old 17th Apr 2021, 04:28
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I would suggest paying attention to your instruments like ADI (sic) as a priority. Too many times I have seen engine power anomalies and/or throttles go unnoticed until the aircraft itself now confuses the pilots
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Old 17th Apr 2021, 05:40
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Page 8, Post #148 seems relevant once more.
Re: Originally Posted by Buswinker View Post
Question, I read the flight was scheduled to be operated by an -800 and the -500 was a last minute swap in. Would the same crew operate both? Are there significant enough differences between the two for that to cause issues?
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Old 17th Apr 2021, 08:54
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tdracer, re AT clutch / cable description #792.
Is it possible, depending on design, for both thrust levers to move together - AT clutch control in flight deck area, but with cable friction etc, for one engine to lag or freeze resulting in asymmetric thrust.

Joe999, look at the engine instruments to get a better indication of what is happening rather than the input thrust levers. e.g. check the room light is on, not assume that it should be based on the switch position.
Same for aircraft with auto-pilot; look at what the aircraft is actually doing - instruments, opposed to what it should do according to a mode annunciator. cf lomapaseo #795

joilhokistix, #796, leading to an interesting point on differences training.
Normally same/common type training progresses from the older variant to the newer one with differences training. However, with some regulatory interpretations it is possible to be rated on the latest variant and with ill-determined backwards differences training, also fly older aircraft.
What is the industry experience of this.

Last edited by safetypee; 17th Apr 2021 at 16:24.
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Old 17th Apr 2021, 09:26
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Intruder

is that true? Unless it was on the deferred defect list, they could only have known about a recurrent complaint if they scrolled back in the old logs and that is not mandatory.
off course it is good practice to do so, but is not mandatory. And it is one of the first tasks that will slip when you are in a time squeeze..
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Old 17th Apr 2021, 10:47
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Some may remember the Tarom A-310 crash that had a double emergency according to the accident report. At the same time that the captain became incapacitated, there was an autothrottle malfunction. According the report, upon noticing that the captain had a problem, an attempt was made to select the autopilot on but it tripped off. The F/O did not notice the unusual aircraft attitude in a timely manner as the aircraft was in IMC.

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Old 17th Apr 2021, 14:51
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golfyankeesierra

If you consider a review of recent maintenance actions as "not mandatory", I don't want to fly in your airplane!
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Old 17th Apr 2021, 15:27
  #798 (permalink)  
 
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ok, if it is mandatory to scroll back your logs for maintenance actions, how far do you have to scroll back? One flight, two flights, a week?
What I am triggered on is that you call others “derelict in their duties” for something that is good practice but not required.
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Old 17th Apr 2021, 16:22
  #799 (permalink)  
 
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I wouldn't even go so far as to call it "good practice". More like ... vaguely interesting. Open defects are enough - I would only look through previous history if I had a problem myself and wanted to see if it looked like a recurring problem.
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Old 17th Apr 2021, 19:36
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Originally Posted by safetypee View Post
tdracer, re AT clutch / cable description #792.
Is it possible, depending on design, for both thrust levers to move together - AT clutch control in flight deck area, but with cable friction etc, for one engine to lag or freeze resulting in asymmetric thrust.
If I understand your question correctly, not really. There is some cable stretch and lost motion in the connections between the throttle and the fuel control, but we're talking the equivalent of maybe a half knob of throttle movement - so while one engine may lag a bit, it shouldn't be enough to cause a serious issue.
With cable engines, there is normally some throttle stagger between the engines - in addition to what I noted above, there are differences in the fuel controls and their 'trim' settings, and (IIRC) on the CFM56-3 engine, the fuel control controls to N2 - not N1 - so to align N1s might require slightly different throttle positions (there is also an analog electronic supervisory control that trims the fuel control to attempt to keep N1 constant as the conditions change). However even with all that, there should be less than a knob of throttle stagger with equal N1s (and maintenance action taken if it gets that large).
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